Recording and reproducing system



J. MILLS RECORDING AND REPRODUGINQ SYSTEM Filed April 23, 1924 bo J5 gQ m l 1 1. 1 l l l O I Amplifier 351 /9 fi Recorder'- :j Trnnsmi'1'1'er A3 /J MVJ 7 iiiil illiii Amplifier 6 l0 Amplifier /5 l l. l l l l l Amplifier Amplifier 9K1 /Z Amplifier Amplifier /7] Patented Nov. -1, 1927.

UNITED STATES PATENT-OFFICE.

JOHN MILLS, OF WYOMING, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMI- PANY, INCORPORATED, OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK.

RECORDING AND REPRODUCING- SYSTEM.

Application filed April 23,

This invention relates to recording and reproducing systems such as phonograph record making or radio broadcast reproducing systems, and particularl to systems for 6 electrically recording speec or music pro- .duced in studios.

In auditoriums sound: proceeds from the source and strikes the boundaries of the room where it is partly reflected and travels out 10 until it reaches another surface where it is again partly'reflected. At each impact some of the energy of the sound is absorbed or transmitted by the surface so that the reflected sound is weaker than the original.

The result is that a succession of tones of diminishing intensity are produced which afi'ect the listeners car so as to give him the impression that the original sound dies out slowly. This eflect is called reverberation 2e and is evidenced by the persistence of the sound'after the emission of the sound by its source has ceased. In the study of the acoustics of auditoriums, it has been found that a considerable time of reverberation is' desirable for music, since the blending of the tones produces a pleasant effect.

In the making of phonograph records, radio broadcasting, and the like it is often desirable to produce music in small rooms or studios. In such rooms the walls are so close to the source of the sound that if natural reverberation were permitted, the reflectedsounds would follow each other in such rapid succession that a confusion of tones rather than a'pleasant blending would result. It is, therefore, the usual practice to provide the studios with draperies that absorb rather than reflect the sound. Vilhile by a proper arrangement of the draperies, the room may ;be made to have a desired time of reverberation this does not cause the studio to simulate the acoustic propertiesof a large auditorium. For one reason the distance of the auditor to the reflecting surfaces is so small that the component sounds follow each other in such rapid succession that an entirely difierent efiect is produced than in an auditorium where the distances are much greater. The result is that when music such as orchestral music which one is accustomed to hear produced in large halls is produced in a studio the effect is unnatural.

It is an object of this invention to improve the quality of music produced in studios.

embodiment of the invention in which re- VGI'lOQI'aiJIOH is produced by the reflection of 1924. Serial No. 708,372.

It is a further object of this invention to simulate in music roduced in small rooms the effect and quality of music produced in largehalls.

It is a further object of the invention to PIOVldB electrical means for' producing artific1al reverberation in music produced under cond1t1ons which tend to eliminate natural reverberation.

In accordance with this invention the quality of music produced in acoustically dead room's 1s 1mproved by producing artificial reverberation. As is well understood by those skilled in the art, artificial trans- IIllSSlOIl lines cause both an attenuation and a phase shift If they are so designed that the phase shlftis proportional to the frequency the wave is not distorted but merely delayed 1n time of transmission. It is therefore proposed to make use of these properties of artificial lines for roducing reverberation in recorded music. 11 one form'this invention comprises an electric recording system zY-lth artificial lines for producing reverbera- A feature of this invention consists in transmitting waves over an artificial line refleet ng them at the distant end and transmittlng them back thus obtaining twice the phase shift on delay which could be obtamed by transmitting them over the line 1n only one direction.

A further feature of the invention consists n amplifying the waves at the distant end 1n connection with this reflection.

ThlS invention will be more readily understood by reference to the following description in connection with the drawing in which: Fig. 1 shows diagrammatically, one

electric Waves in an artificial line. Fig. 2 shows a second embodiment which employs a standard 21 type repeater circuit in connection with an artificial line. Fig. 3 shows a third embodiment which employs a series of parallel paths comprising artificial lines of dilferent length.

The description of Figs. 1 and 2 which follows will be more readily understood after referring to the following description of Fig.

3. There is shown a transmitter 5 on which the sound is impressed. Connected to this is an amplifier 6, and to the output of the amplifier are connected various parallel ample ing telephone receiver,

puts of the am paths 7, 8 and 9. Amplifiers 10, 11 and 12 are connected in these paths. Paths 7 and 8 are provided with artificial lines 13 and 14, respectively. The terminals of these .hnes are connected to the ampllfiers 15 and 16, respectively, while an amplifier 17 1s provided at the far end of the path 9. The outlifiers 15, 16 and 17 are connected in para lel' through the transformer 18 to a recorder 19 which may be, for exa phonograph recorder, a loud speaka radio broadcasting by means of which it circuit or other device,

the music impressed is desired to reproduce on the transmitter 5.

Part of the waves produced by the transmitter passes directly through path 9 to the recorder, while other parts pass through the two parallel paths 7 and 8. The phase shifts of lines 13 and 14 are so adjusted that the waves fiowin through them arrive at the recorder later t an the waves flowlng through the path 9. The attenuat on of the lines and the degree of amphficationof the amplifiers are so adjusted as to 'make the amplitude of the waves flow ng through the lines smaller than the amplitude of waves passing through path 9. These component currents decreasing in amplitude and laggin in phase produce an effect in the recorder similar to that which would be produced by a natural reverberation in an auditorium.

It is evident that as many parallel paths may be used as desired giving any desired number of component currents. Since it is often advantageous to be able to regulate the reverberation to suit the type of music recorded and the type of hall it is desired to simulate, it may be desirable'to use artificial lines of the variable type such as those disclosed in my United States Patent No. 1,628,992, issued May 17, 1927, and so permit the time interval and rate of decay of the reverberations to be adjusted to suit the individual requirements of each recording.

In the embodiment shown in Fig. 1 a

transmitter 21 is connected through a transformer 22 to an amplifier 23, the output of which is connected through a second transformer 24 to a potentiometer 25. Connected to the potentiometer are two parallel paths, one comprising an amplifier 26, the output of which is connected to the recorder 29' and the other comprising an artificial line 27, the terminal 28 of which is left open.

The wave flows from the transmitter through the, first amplifier to the potentiometer where it divides between the two parallel paths, part going from the amplifier 26 to the recorder 29, the other part.

passing into the artificial line 27. This part flows through to the open terminal where it is reflected back through the line, being attenuated and retarded in phase as it passes in each direction. When the reflected wave reaches the potentiometer 25, part divides between the input circuit of the amplifier 26 and the output circuit of the amplifier 23 and part is reflected back into the artificial line, which is so constructed thatits impedance does not match the impedance of the potentiometer. The current which passes into the output circuit of the amplifier 23 is dissipated, while that which passes into amplifier 26 is amplified and passes on to the recorder 29. This current is smaller in amplitude than, and lags behind, the original current flowing into the recorder. That part of the wave which is reflected back into the line repeats the cyclefollowed by the first wave flowing into the line, thus causing a third component current to flow into the reproducer. This third current is still smaller in amplitude and still further lags behind the original current. In this way a series of component currents each decreasing in amplitude and each lagging behind the other are produced.

In Fig. 2 a transmitter 31 is connected to circuit 32 which is, in turn, connected' through an artificial line 33 to a second 21- type repeater circuit 34 and thence through an amplifier 35 to a recorder 36. Part of the current coming from the transmitter 31 is transmitted directly to the artificial line 33, but the larger part divides between the input and output circuits of the vacuum tube amplifier 37. The energy which flows into the output circuit is lost. The wave flowing into the input circuit is amplified and the amplified current passes to the output coil 38 where it divides between the transmitter circuit and the artificial line, half going to each, if the impedances of 31 lOfl and 33 are balanced which must be substantially the case in order to avoid singing. The energy of that half which passes into the transmitter circuit is dissipated, while the wave flowing into the artificial line goes to the repeater 34 where it is amplified and the amplified current passes to the output coil where it divides between the recorder circuit and the artificial line. The wave which flows back into the artificial line is amplified by repeater 32 and half of the amplified current dissipated in the transmitter circuit, while the other half passes into the artificial line and is amplified by repeater 34, half of the amplified current passing back into the artificial line to repeat the cycle, while the other half flows into the reproducer circuit. This last current lags behind the original and is of smaller amplitude due to the phase shift and attenuation of the artificial line and so appears as the first reflection. Part of the current which flows back into the line is also finally impressed on the reproducer after having the amplificationof the repeaters may be adjusted to give the desired effect.

As pointed out above this invention is widely applicable to various systems for recording and'reproducing sound and it should be understood that the terms recording sys tem and recorder as used in this description and the appended claims are meant to include all such systems and devices.

Many embodiments of the invention will readily-suggest themselves to those skilled in the art and the invention is not limitedv to the three examples shown.

What is claimed is:

- 1. In combination, means for producing waves corresponding to sound and a phase shifting wave transmission system associated therewith for producing artificial reverberation..

2'. In combination, a telephonetransmitter and an artificial line in circuit therewith for producing the elfects of reverberation in the electrical waves.

3. A sound recording system, comprising. a telephone transmitter, a recorder and an artificial line for producing reverberation, connected in circuit therewith.

4. A sound recording system, comprising a telephone transmitter, a recorder, and means comprising an artificial line for producin reverberation of the recorded sound.

5. sound recording system, comprising a telephone transmitter, an electrical recorder, and a plurality of wave transmitting paths associated with said transmitter and recordgr, one of said paths including an artificial 6. A sound recording system, comprising a transmitter, a recorder, and a circuit associated with said transmitter and recorder comprising an artificial line, whereby component currents of different phase and amplitude are impressed on said recorder.

7. A sound recording system comprising a transmitter, two paths connected in parallel to said transmitter, an open ended artificial line connected inone of said paths, and a recorder connected in the other of said paths. I

8. A system for recording sound produced under conditions which tend to eliminate reverberation comprising means for converting the mechanical vibrations which comprise the sound into electrical waves, means for reconverting said electrical waves into mechanical vibrations, and means associated with said converting means and said reconverting means for producing the slow dyingout of said electrical waves, whereby substantially the same effect is produced in said reconverted vibrations as would be produced had the sound originally been produced under conditions of natural reverberation.

9. A system for recording sound produced in acoustically dead rooms comprising a transmitter, a recorder, a variable ratio amplifier, and a variable length artificial line associated with said transmitter and recorder for producing the desired reverberation ofsaid recorded sound.

10. An apparatus for producing a desireddegree of change in energy waves comprismg a wave transmission system for producing a portion of the desired change, means for impressing the waves on said system, and means for reflecting the waves back through the system to eflfect another portion of the change, said wave transmission system being proportioned in accordance with the degree of change it is desired to produce.

11 In combination, a network for efi'ect- 'ing a phase shift on waves transmitted theret-hrough, a two way one element type repeater associated with said network to amplify and reflect the waves back through said network to multiply the phase shift produced therein.

12. In combination, means or converting sound waves produced in an acoustically dead room into corresponding energy waves of a different type, and means associated therewith for modifying the converted waves to simulate natural room reverberation.

13. An apparatus for producing a desired time delay in the transmission of energy waves, comprising an artificial line proportioned to produce in a single traverse a predetermined fraction of the desired time delay, means for imprssing'the waves upon said line, and means at the remote line terminals for retransmitting thereceived waves back through the line to produce another fraction of the desired delay.

14. An apparatus for producing a desired time delay 111 the transmission of energy waves, comprising an artificial line proportioned to produce in a single traverse a predetermined fraction of the desired time delay, means for impressing-the waves upon 7.

JOHN MILLS. 

